texts:
Assume you are given a star map that doesn't have the name of the stars on it. You know the latitude, longitude of the observer and the local time (year, month, day, local time). How could I proceed to find the stars, planets?

Notes: This requirement is given by a problem with the photo shown above. You cannot go outside, nor use other resources.
The stellar map represents the sky of a city ($44^\circ 26'$ N, $26^\circ 06'$ E, local time 00:47, date 04.03.2016).

Mark on the map the cardinal points
Identify on the map the planets from the solar system
Identify Polaris
Identy the circumpolarity zone. Identify at least 2 constellations outside the zone
Find the galactic equator and the ecliptic


texts: Stars can easily fuse atoms to give of heat and radiation. But at Wikipedia it said that only sub-iron atoms give of energy when fused and take energy when split, and post-iron atoms is the exact opposite. So, if enough heavy elements got together could a "reverse star" be made in which it gives of light and heat through means of fission? How long would such a star last, and why aren't they common, if they even exist?


texts:
What appears to be a string of satellites moving nearly overhead towards NW at 10:30pm to 10:50pm Near Eagle River WI on Sun May 26, 2019.

Was lead by 3 equally spaced (approx 1/2 in total length of three at arms length), appro magnitude 4-3.  A couple of min later approx 10 other objects followed in the same line but much dimmer.

Clear night. No Moon.

What was this phenomenon?


texts: What does it mean when there are two plus-or-minus signs for a measurement?

texts:
As far as I know, the plus-or-minus sign is used to indicate the statistical margin of error of a measurement. But what does it mean when there are two plus-or-minus signs in the same measurement?

Some examples from Wikipedia:

The mass of M87* is given as (6.5 ± 0.2stat ± 0.7sys) × 109 M☉ (as measured by the Event Horizon Telescope).
The measured distance to Sagittarius A* is given as 7860 ± 140 ± 40 pc.


texts: When we say a variable star is "fainting" does it mean something more or different than "dimming" or "fading"?

texts:
A comment below the question Does the current “fainting” of Betelgeuse show any spectral trends that differ from it's normal variability? suggests that "dimming" would be a better term, but I have a hunch that the use of the term "fainting" in this context is more than just a choice of synonyms for decreasing in brightness.

A quick check in google scholar for "variable star fainting" returns many results that seem to use fainting in deliberate way.

Question: When we say a variable star is "fainting" does it mean more or different than "dimming" or "fading"?

"bonus points" for any history on the term; was it first used by someone speaking proper English rather than that horrible derivative they speak in the US? ;-)

If we don't get an authoritative answer here in Astronomy SE in a few days, I'll think about moving this to English SE or History of Science and Math SE.

In the mean time it would be great if people could refrain from:

suggesting it would be "better asked" elsewhere
posting speculative or low-quality answers, which will make it impossible for me to then move the question by myself

Thanks!


texts: A neutron star without a flat surface and an atmosphere?

texts:
In the Kurzgesagt video Atoms As Big As Mountains — Neutron Stars Explained they state that neutron stars have an atmosphere that reaches about 10 centimeters above the surface.

How is this possible? Wouldn't the strong surface gravity pull all of the material onto the surface of the star?

Further, Kurzgesagt also states that the neutron star has a surface variation of about 5mm. Still, wouldn't gravity pull it flat? Of is the gravity not strong enough to do so?


texts: Parking a telescope at a Lagrange point: is this a good idea from a debris point of view?

texts:
The James Webb space telescope is supposed to be located at the Earth-Sun L2 Lagrange point.

Do we expect the region around that point to have a higher concentration of space debris, asteroids, dust, etc...? Would this be a matter of concern for bringing the telescope safely in position (i.e. require extra dust shield)? Do we expect however the exact Lagrange point to be free of any matter since it would take an acceleartion/deceleration for matter to actually reach that exact location? How large would be this 'debris-free' zone?


texts:
I read that solar flares are customarily viewed in H-alpha light, as a temporary brightening of a small portion of chromosphere.

What all can be interpreted from this? Is it because, energy of the radiation contained by the flare lies around this wavelength? And why chromosphere ?


texts: What is it like at the edge of the universe?

texts: If the universe is expanding, then if you were to be close to the edge of that expansion, what would it look like? What would be happening? Would it be chaotic? Would objects be appearing or disappearing? I don't even know if it's possible to have any knowledge of this, but I'd like to know if there are any theories.


texts: Cosmological density fluctuation dependence on scale factor

texts: I want to show that in the radiation-dominated era, $\delta_H^2 \propto a^{1-n}$. I know that the wavenumber corresponding to the Hubble scale goes like $a^{-1}$ and that $\delta_H^2 \propto k^3 P(k)$ and $P(k) \propto k^n$, but I am unsure of how to put these together to get the desired result.


texts: Why is Saturn the only large planet without any trojans?

texts:
Every planet apart from Mercury and Saturn has trojans in its L4 and/or L5 points.
Mercury is easy enough to explain: It is small, has an eccentric orbit that precesses, and any trojans it has would be heavily perturbed by the Sun's gravity.
However Saturn doesn't have any of those complications. The answer given to this question is that Jupiter's gravity perturbs any trojans at Saturn's L4 and L5 points.
But if Mars, which is much less massive than Saturn and comes closer to Jupiter, can have multiple trojans then there's no reason why Saturn shouldn't.


texts: Dobsonian telescopes: do collapsible scopes have any drawbacks?

texts:
When choosing between a collapsible and a non collapsible 12” dobsonian scope what drawbacks if any do collapsible dobsonian scopes have?
If I transport any scope it will need collimating. Obviously a collapsible scope will store better.


texts: Finding luminosity of a star with magnitude

texts:
I'm working on my assessment for Physics in the IB, and I'm planning to investigate stars in spiral galaxies and determine their ages. For this I'm going to use data from the SDSS (Sloan digital sky survey http://skyserver.sdss.org/dr13/en/tools/chart/navi.aspx).

I need to get the luminosity of a star from the absolute bolometric magnitude. However the SDSS only gives magnitude in 5 values, u g r i and z. I've tried to understand what to do with these and what they mean but I can't figure it out.

How would I get one number the absolute bolometric magnitude from 5 different values, and what do they mean?


texts: I have gotten LightKurve to work and plot a lightcurve to allow for the identification of possible transits. However is there a way I can get it to run and tell me if there is a possible transit in the data? I know this possible as at TESS they don't go through all the graphs manually but I don't quite know how to do this? If not is there another package that will do this?


texts: Units in optical and radio spectral data cubes: Flux vs Brightness

texts:
I have noticed that the units used in spectral data cubes coming from optical IFU instruments are usually in $erg/s/cm^2/Ang/pixel$. To my understanding this is a measure of Flux. Right?

However, in radio astronomy, spectral data cubes coming from interferometers is usually in $Jy/beam$. To my understanding, this is a measure of surface brightness. Right?

Why optical and radio spectral data cubes don't use the same kind of unit (either flux or brightness)?


texts: How did Ptolemy prove in the following excerpt that the Earth is not cylindrical?

texts:
I have trouble interpreting the following excerpt:

  “Nor could it [the Earth] be cylindrical, with the curved surface in the east-west direction, and the flat sides towards the poles of the universe, which some might suppose more plausible. This is clear from the following: for those living on the curved surface none of the stars would be ever-visible, but either all stars would rise and set for all observers, or the same stars, for an equal [celestial] distance from each of the poles, would always be invisible for all observers.”

I understand that if the Sun rotated around the curved side of the cylinder, no one living on the curved side would see any ever-visible stars because their view of the celestial views is blocked. However Ptolemy states that “all stars would rise and set for all observers,” which I believe would be wrong because the two poles and the curved surface would be oriented in different directions on a cylinder. He also states that the other possibility is that “the same stars, for an equal [celestial] distance from each of the poles, would always be invisible for all observers.” However, I don’t understand how his explanation in the excerpt directly above would prove that “the same stars… would always be invisible for all observers.”

Here’s the link to my source (page 41, chapter 5:) https://isidore.co/calibre/get/pdf/Ptolemy%26%2339%3Bs%20Almagest%20-%20Ptolemy%2C%20Claudius%20%26amp%3B%20Toomer%2C%20G.%20J__5114.pdf


texts: If the Universe is infinite, why isn't it of infinite density?

texts:
If we make the assumption that the Universe is infinite, and has an infinite number of hydrogen atoms, then why is it not of infinite density - because, under Schrodinger's wave equation the probability of an electron being at any given point is non-zero and any non-zero number multiplied by infinity is itself infinity?

Is the answer (a) I have made some basic error in physics, (b) the Universe is provably not infinite because of this - effectively a version of Obler's Paradox or (c) the Pauli exclusion principle means that electrons just cannot be anywhere?


texts: Measures for the degeneracy from protons?

texts:
Come to think of it, the only things we hear about degeneracy is neutron and electron.
I made a generalization:

White Dwarf: Supported by electron degeneracy.
Neutron Star: Supported by neutron degeneracy and nuclear forces, and sometimes centrifugal force.
Quark Star: Most likely supported by quark degeneracy.

Now, we can see that there is no mention of proton degeneracy.

A quick search lead to the Wikipedia subsection Degenerate matter; Proton degeneracy, and the answer that yes, there is proton degeneracy, but is much less effective than other forms of degenerate matter.

My question: What is the force exerted by degenerate protons, and what equation is it modeled by?


texts: What is the largest (angular) dark area in the sky?

texts:
Question

Within our current knowledge, what is the largest (circular, say) area in the sky which is empty/dark? I'm thinking in terms of angular size.

Motivation

I was wondering what was the largest star as seen from the Earth, other than the Sun of course, in terms of milliarcseconds, say. A search quickly turned up R Doradus which is huge (57 mas as seen from the Earth). But I wondered if it was possible to rule out any (angularly) larger dark objects by finding stars whose light would be blocked if there was such an object.

Of course we should eventually be able to rule out each such area -- as Hubble Deep Field showed, if you look long enough there's a lot to find everywhere -- but relative to our current knowledge, what are the largest gaps?

I expect that the answer would be in a region which has been missed by a sky survey and which coincidentally doesn't have anything we can see.


texts: Why does the Fourier transform of this CMB image have a hole in it?

texts:
The BBC's Desert telescope takes aim at ageing our Universe contains the image below of the Cosmic Microwave Background from the Atacama Cosmology Telescope or ACT. It looks like this is plotted with a diverging colormap which makes sense since they've likely subtracted off the average temperature and probably at least its dipole component if not more (CMBR dipole anisotropy (ℓ = 1)
But looking at it closely, I thought I noticed a strange regularity to the spatial scale, so I downloaded it and imported into Python and took the Fourier transform to see what I'd find.
Despite this being an ugly and very unscientific analysis, I'm still seeing both a sharp cutoff below a spatial frequency of 1.0 inverse degrees, and "ringing" or $J_1$ Bessel-like ripples at higher frequencies.
Are either or both of these profound and important to the analysis, or an instrumental artifact, or something else?

Image in the BBC news item is a JPEG and you can see the subfield discontinuities (part of the way the JPEG wavelets are implemented) once the the thee RGB color channels are separated, but this is a square grid and not related to the clearly circular patterns in the Fourier transform.

Python script: https://pastebin.com/t52VbqeD
Exported image converted to PNG: https://i.stack.imgur.com/BC87Y.png


texts:
How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us?
The question might look a bit odd but I am really stuck on my head. We know, scientists (with tools) explored physically only our solar system and some parts of our galaxy which is really a tiny part of the observable universe. And now they are constantly using these knowledge along with 'tested physical laws' to measure the properties of distant parts of our universe.
For example, we tested and found the speed of the light is constant within our local periphery many times (within our Earth and Space around Earth). But yet we presume that the speed of the light is constant even at the farthest part of our universe. Certainly we did not test it in the other distant part of the universe because we have no way until now. Not only light but also the other physical properties like, luminosity, gravity, and etc related physical laws are agreed upon based on tests within our solar system. And based on these laws we deduced the properties of other parts of the universe (i.e. age, distance, mass, luminosity of stars in millions/billions light years away).
My question is, how do we know that these physical laws which we tested within a tiny area of the universe are consistently working in the distant parts of it? Is there any probability that the distant part of our universe obeys physical laws differently and our prediction based on applied physical laws gave us an unreal illusion of the actual reality, yet consistently?


texts: What is that void that the universe is growing into?

texts:
We understand that this is the universe and it is essentially full of space and time, but what is on the outside of the universe, and isn't that nothing, something, and how far does that reach.

I.e. isn't that another aspect of the universe? For it to go into it, it must be something for it to go into it.

If I throw a ball through the air, the ball travels through air. If I throw a universe through the air so to speak, doesn't that have a characteristic, frame and limitation?


texts:
For mass transfer in a binary system, one star must fill its Roche lobe. What determines whether a star in a binary system will fill its Roche Lobe? How will I calculate it?
I can't find any mathematical formula that shows any equation of mass transfer.


texts: What are the small things, look like stars, moving in the sky?

texts:
I have always been observing something that looks like a star but not as bright as a star moving from south to north at the same time every night.

What is it? It cannot be a star because I know stars do not move.


texts:
I have just been watching a podcast called "Deep Astronomy" and the discussion was about a super fast spinning black hole discovered with the NuSTAR space observatory. This black hole was modeled with high confidence to be spinning at about 99% of the maximum spin rate. They stopped short of saying that the tangential velocity of this spin rate is "c" (and how can a singularity have a "tangential velocity"?) They did say that the event horizon at maximum spin of a stellar black hole is about 1-1/2 km. and that if a black hole were to spin faster then the result would be a "naked black hole" that would defy the laws of physics (GR).

Also, shouldn't all black holes spin extremely fast (conservation of angular momentum) or would a retrograde accretion disk slow it down. Could somebody clarify this whole "black hole spin thing" without getting too complicated??


texts: Why is CMB an evidence of hotter and denser early Universe?

texts:
In his book Gravitation and cosmology, Steven Weinberg says that CMB makes it  "difficult to doubt that the universe has evolved from a hotter denser early stage".
In my understanding, CMB is just a peculiar isotropic radiation representing a black body at ~ 2.7K.
How and why does CMB point to the early Universe being hotter and denser?
[The interested reader may refer to answers on Physics SE.]


texts: Where does the radiation in space come from and can we observe it?

texts:
I have recently been reading that space travel is strongly influenced by "space radiation" and how it poses a threat to human space exploration.

Does this radiation originate from stars like our Sun, or is it an omnipresent — let's just call it — "force" in space (such as cosmic noise) that doesn't have any specific source?

Also, can an amateur astronomer visualize this radiation in some way so as to be able to observe it?


texts: Does the sun have a protective layer that at least diminishes its radiation. I know the earth's atmosphere protects us from harmful rays. But does the sun have a sort of shield as well that if removed would radiate more heat.


texts: We know that an object falling to the black hole, as observed from an observer far away, will freeze as it gets closer and closer to the event horizon. So my question is how can a black hole form in the first place? I mean we usually say thing a star collapses into a blackhole. But considering the effect of "time-freezing", how could that be possible in the first place?


texts: Can the Sun become a big ball of gold atoms?

texts: The atoms inside the core of sun are continuously fusing and forming other atoms. Can this continuous fusing make gold atoms?


texts: Do planetary rings have geometric bounds?

texts:
Are there any bounds on where a planetary ring can form and maintain orbit relative to the planet?

Do they have to be in a circular equatorial orbit?

Is there a min or max altitude, say with respect to the Roche limit, geosynchronous orbit, or other points in space?


texts: How did LIGO verify that the gravitational waves originated 1.3 billion years ago from two specific black hole collision?

texts:
So they finally found gravitational waves.  That's cool and I trust is the case, but how did they confirm it originated 1.3 billion years ago and that two blackholes merging caused it and what distance it came from?

I am not sure if the extent of variation in the laser wavelength can tell us all this above information..

Any clues ?


texts:
Good day folks.
My Grandson would like to start using this Telescope Celestron Nexstar GT102, has been in the basement for years, and unfortunately, we appear to have misplaced the eyepieces.
Just wondering if anyone had any insight what would be a reasonable eyepiece for me to buy so he can see the moon at the very least decently enough.
Also, would Amazon be a good start for eyepieces that way I can get them fairly cheap and quick.
Thanks in advance


texts: Why does the star formation rate correlate with the total stellar mass in star forming galaxies?

texts:
The so-called "Main Sequence" of star-forming galaxies (e.g., Brinchmann et al. 2004; Noeske et al. 2007) clearly points to a linear relation between the stellar mass of galaxies and their star formation rate.
This relation holds at all redshifts, with a time-evolving normalisation.
The question is: what is the physical reason why, at a given time, the total stellar mass (which is an integrated quantity, i.e., the integral of the past star formation history if you want) should be linearly related to the rate at which stars are forming?


texts: Does New Moon Affect Stargazing After MoonSet?

texts:
Referencing the following data for December 11th 2017.

https://www.timeanddate.com/moon/@4799274?month=12&year=2017

To get a dark sky for stargazing does it matter if the moon is at 37.8% so long as it is below the horizon when I'm observing?

Since the moon will be set at 1:32PM on the 11th and not rise again until 1:59AM on the 12th I would assume the moon would not affect viewing between those times.

Furthermore is there a guideline as to how close to moonrise the moon will start to have an affect?


texts: Astronomy & machine learning. Where to start?

texts: I am a Computer Engineering major and would like to learn more about machine learning methods in Astronomy. What books or other resources could I use?


texts: Gravitational acceleration inside a planet

texts:
The gravitational acceleration, g, inside the Earth generally decreases with decreasing distance to the center:

However, apparently for Jupiter, the gravitational acceleration only increases with decreasing distance to its center. Why is this?


texts:
I have the orbital elements of an asteroid's heliocentric motion (the orbit has non-zero inclination and is elliptical). But I want to simulate the motion of the sun around the asteroid. So without having the sun's ephemeris, and given only the asteroid's orbital elements, how can I determine an equivalent orbital elements for the sun's motion around the asteroid?

Edit:
I realize that the question wasn't clear enough based on the comment. So, what I am trying to do is to numerically solve the two body problem equation in the inertial frame. In the classic two-body problem 2nd order ODE, in my case, the position vector is defined from the centre of the asteroid to the sun, which is absolutely valid and upon integration gives me the position an velocity for the sun with respect to an inertial frame centred at the asteroid. My question is concerned with the initial conditions to begin the numerical integration. As of now I determine the initial state vector for the Sun from some random orbital elements. But to perform a more realistic simulation, Is it possible to determine the real orbital elements for the asteroid-centric motion of the Sun from a given set of orbital elements of a heliocentric-motion of the asteroid? I hope I was clear and not made this more confusing.


texts: What azimuth description systems are in use?

texts:
For a time, I thought Azimuth is always direction in degrees, 0 for local, geographic north, 90 for east etc.

Then, trying to observe moonrise I downloaded an app that gave azimuth in values between (if I recall correctly) -180 and 180, and I think "0" corresponded to south. I tried to read up on that and found very little fragmented information. I found other resources that frustrated me with numbers greater than 360, or provided values commonly associated with "West" for azimuth of moonrise and generally it took a bit of searching to find something with plain "degrees from north"

Could someone either post or provide a link to a comprehensive guide to various azimuth angle systems, when and where they are in use, and how to recognize which one is used?


texts: If the fifth gas giant in the early Solar System was completely ejected, where would it be now?

texts: I've read about the possible 5th gas giant in the Solar System, and about its ejection about ~100 million years after the formation of the Solar System. However, I have not seen anything about its potential whereabouts. Assume this gas giant (let's call it G5) was completely ejected from the solar system. Would G5 still remain in the vicinity (100 ly or less) or would it be very far away from the Sun right now?


texts: What will the universe be like in a googolplex years time?

texts:
It will be cold and dark in 10^(10^100) years.

What else can be said of the state of things in the far distant future? Will everything have fallen into supermassive black holes and then radiated back into space so there is no matter left?

Will the universe revert to an exotic state as it was in primordial times, or will it slow and stay unchanged indefinitely? What kind of structure will it have?


texts:
As observed from the surface of Earth:
Will the moon ever repeat the same path (trajectory)?
If yes, what is the period of repetition?
And also will the moon cover the night sky with its path completely over a period of time?

More explanation:
I was observing the moon from my window and I was wondering will the moon follow the same path (trajectory) as it did before, and if I am taking photos all the different positions of the moon over a long period of time will it have covered the night sky?


texts: Calculate object apparent diameter by distance and radius

texts: I'm trying to create a dynamic starfield for game using the HYG database. Because there are no data about the apparent size of the stars from earth, I will need to get it myself. I found a formula which calculate the radius by the temperature and the luminosity of the star. It's working, but the problem is that because a lot of stars are very far, I normalize the distance of the stars so they are all at the same distance in the game engine(they form a dome around the scene). I'm looking for a way to set the size of the stars in the sky, even if normalized, using the radius of the stars, and the real distance from earth. I tried: Distance / radius, but the size of the stars make no sense, betelgeuse is 10 times larger than bellatrix, but they should be almost equivalent.


texts: Do the neutrons in neutron stars emit the radio waves?

texts:
Neutrons can, especially in extreme circumstances (and large concentrations) emit electromagnetic radiation. I specifically asked about this in Physics S.E. Has a free neutron ever been shown to absorb/emit/interact with a photon?, the answer has to do with the fact that although neutrons have no detectable electric moment or dipole, they DO have a small, 'negative' magnetic moment.
But little I have read about neutron stars says which particles in or around them emits the radio waves, except one brief article mentioning infalling electrons from a surrounding plasma.


texts: How to interprete function value of get_sun in astropy

texts:
As I know, spring equinox of 2016 is on 2016/3/20 4:30 GMT.

I execute following statements in python:

```

from astropy.time import Time

from astropy.coordinates import get_sun

t=Time('2016-03-20 4:30:00')

s=get_sun(t)

```

I expect to get s.ra.degree and s.dec.degree very close to 0.

But I got s.ra.degree=0.7052336 and s.dec.degree=0.30536325.

Why?

Hope some one can help me. Thanks.


texts:
If I had a directional photon-emitting source and placed it inside a black hole pointing upward and out towards the visible universe, I assume the photons traveling at the speed of light would slow and reverse direction back into the center.

So if I took the same source and placed it outside of the black hole pointing inward towards the black hole center, can I assume that an emitted photon would travel towards the center faster than the speed of light it is already traveling at?


texts: If space is negative energy and matter is positive energy then does that mean the universe is finite?

texts: I was reading a book by Stephen Hawking, it was written that universe is made up of 2 ingredients,i.e., space and energy and space was the negative energy, so they add up to 0. But since space is energy does that mean it is finite?


texts: Radial velocity exoplanet search - can mathematical details be explained? (Bayesian periodogram MCMC)

texts:
Radial velocity (RV) is one of main methods for exoplanet search.
The popular description of the method sounds simple - one should measure periodic Doppler variation of a spectral line of a star and determine characteristics of orbiting planet (period, minimal mass, etc).
But if you read scientific articles (like this about Proxima b) - the picture is different.
Image from the article:

My current understanding:
A telescope with high-resolution spectrometer observes a specific spectral line of a star. The result is in pairs (Vi,Ti), i=1..N. Here Vi are Doppler variations of radial velocities and Ti are times of observation. Ti are transformed to barycentric times.
Astronomers then use a model to search for a hypothetical planet such that it has a much higher Bayesian probability than model without planet. Much higher usually means 10000 higher in modern publications. If some Keplerian solution (planet's period, mass, eccentricity) satisfies the threshold - one "planet candidate" is found. Let's subtract it from the observations and search is there still high Bayesian probability of another planet.
But I still can't figure out how the math in done.
Questions:*

Can mathematical details of the method be explained in simple terms? This work contains some details, but from it I can't understand what is being done.

Does complete review of RV method exist online in free access?

How exactly is the math done?  How does Markov chain Monte Carlo (MCMC) "scan" possible parameters of planet's orbits?

How exactly are Bayesian periodograms built?

EDIT
Question:
Does complete review of RV method exist online in free access to read about the details?


texts: Why does the Moon stablize Earth's axis?

texts:
In an academic study titled 'The Moon and the Origin of Life on Earth'  it is said that

  'If the Moon did not exist, the orientation of the Earth’s axis would not be stable, and would be subject to large chaotic variations over the ages. The resulting climatic changes very likely would have markedly disturbed the development of organized life'.

Since I don't have enough physics and mathematics knowledge in order to understand why the Moon stabilizes the Earth's axis, can anybody explain in simple words this phenomenon?


texts:
What color is earthshine (e.g the average color of earth that shines on the moon)?  I am making a solar system exploration game, and would like to know this for the lighting of my moon level at night, with a "full earth".

Edit: With your answers, this is what I get:

Edit:
Here is a video including the moon level, bathed in earthshine as the specified color in the answer at "night time" (clip is 12 seconds into the video):
https://www.youtube.com/watch?v=HKGCtkps8gk&list=PL9Bk1v7iJfdCpRaQ6vTGYOM-lXAO7RAQ1&index=1

If interested in my game I am making, here is a link to it:
https://jonathanlcopeland.wixsite.com/planetary


texts: (How) Can one determine if an exoplanet is synchronously tidally locked or not?

texts:
Mercury is asynchronously tidally locked so that all of its surface regularly sees the Sun. But an exoplanet which is synchronously locked to its star, could we tell that it is? It would have a hot side and a cold side. This should affect transit and occultation on some wavelengths, but does the symmetry of the movement degenerate any possibility to disentangle tidal locking from that?

Mercury seems to cool down during night time, and gas giants maybe distribute their temperature atmospherically. So their tidal locking might be hard to discern. But there are terrestrial exoplanets with much shorter orbital period which should have a cool side and a hot side permanently. That's my speculation. My basic curiosity is:

Is Mercury a freak or a standard in terms of tidally locked planets being asynchronously so? And by observational support, not just models.


texts: How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

texts:
Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms between neighboring array elements i and i+1, this won't be the same as the difference in Angstroms between any other two neighboring elements j and j+1. However, if I first took the log10 of the wavelength array, then the difference between any two neighboring logarithmic array elements i and i+1 would be equal to the difference between any other logarithmic array elements j and j+1.

Now, I know a priori that this wavelength array has a velocity offset of X km/s, which I basically want to remove. How do I apply a velocity shift of -X km/s to this wavelength array which has uniform logarithmic spacing?


texts: Why can falling stars only be seen moving down towards horizon not up away from horizon?

texts: Are falling stars as we know only just space debris entering and burning up in the atmosphere and not a star at all?


texts: How are stellar elemental abundances quoted?

texts:
Close to the bottom of page 4 of this article (marked as page 164 in the upper left corner) states

  Values are given in the logarithmic scale usually adopted by astronomers, A$_{e\ell}$ = log N$_{e\ell}$/N$_H$ + 12.0, where N$_{e\ell}$ is the abundance by number.

I have never used stellar elemental abundances in this way, so I want to check a few things.

First of all, is the logarithm used by this paper log$_{10}$ or log$_e$ (often written ln)?  My guess is log$_e$ because of what follows.

Let's say I want to calculate the elemental abundance of He relative to H.  I believe the correct math would be to do the following

$$\frac{\textrm{N}_{He}}{\textrm{N}_H} = \textrm{exp}(\textrm{A}_{He} - 12.0)$$

Is this the correct way to calculate the relative abundances?  This equation gives a value of 0.343 for the helium abundance relative to hydrogen, which seems to be the correct value for the sun (the sun is usually quotes as being about 70% H and about 25% He, which gives a relative abundance of 0.357).  This correct value is what leads me to believe that the log is log$_e$.


texts: Is there a prediction when our solar system would fall apart?

texts:
Within a few billion years our Sun would become a red giant and destroying Mercury and Venus and perhaps even the Earth. But nevertheless our solar system still have some planets like Jupiter and Neptune orbitting around the sun, because his mass wouldn't be very different.

After another while our Sun would turn into a white dwarf. Probably his mass changed a bit, but would it be enough to lose for example Neptune?

If not, is there a prediction at what time, if ever, our 'sun' will lose (some of) his planets for the first time?


texts: I'm looking to make a custom pulsar map like the one on the Voyager Records, but for an arbitrary location within the Milky Way Galaxy. I'm not even sure where to begin.


texts: How do I plot field of view of an earth-based observatory in Galactic Coordinates?

texts:
I would like to plot in Galactic Coordinate the sky field-of-view of an earth-based observatory (e.g. MAGIC). Something like this from Liu et 2016.

I already know how plot source positions on a 2D projection of the sky (following this tutorial: http://learn.astropy.org/plot-catalog.html).
Is there a simple way to plot the field of view using astropy and/or astroplan and/or matplotlib?

Thank you very much for your help


texts: When calculating absolute magnitudes of distant objects, do you use the light-travel distance or the comoving distance?

texts: I want to calculate the absolute magnitude of GN-z11. Its light-travel distance is 13.4 billion ly (4.1 Gpc), its comoving distance is 32 billion ly (9.8 Gpc), and its apparent magnitude is $25.8$. Calculating its absolute magnitude, we get $M=-76.86$ for light-travel, and $M=-94.09$ for comoving. Which one do I use? I am assuming it is the former. Is this correct, or is there a different formula for this?


texts: Understanding date of astronomical events

texts:
I have a masters in chemistry but pretty much, a layman in astronomy.
So, can you please explain to a novice like me, about this paragraph taken from the Wikipedia article on Makar Sankranti:

There are two different systems to calculate the Makara Sankranti date: nirayana (without adjusting for precession of equinoxes, tropical) and sayana (with adjustment, sidereal). The January 14 date is based on the nirayana system, while the sayana system typically computes to about December 23, per most Siddhanta texts for Hindu calendars.

Am I correct to understand that when the date was assigned in Hinduism some thousand (?) years back, the winter solistice used to be on 14th/15th January?


texts: Why do we observe spectral lines of specific energy?

texts:
The basis of my confusion is that atomic orbitals, even when described accurately by quantum numbers, have definite energies, meaning they represent energy eigenstates of the wave function. They're stationary states, and thus separable solutions to the Schrödinger equation. The general wave function of an electron, however, is a linear combination of such states, so that general solution does not have a definite energy. Still, we observe discrete spectral lines at specific wavelengths (with some broadening).

Why do we observe spectral lines of specific energy when the wave function of the electrons in an atom are linear combinations of energy eigenstates?

It seems like the spectral lines that are observed are just the energy eigenstates, while, according to quantum mechanics, the wave representation of electrons is a linear combination of those states.


texts: Is there a way to estimate or calculate the tidal range induced on a water-bearing planet?

texts:
Consider a system in which a central star is orbited by a planet with liquid water oceans, which is itself orbited by a moon.
Given the masses and distances between these three objects, is there some formula that outputs the minimum and maximum tide heights the planet's oceans cycle through for every orbit of the moon?
For simplicity, the effects of local topography on the tides are being ignored.
Also, if there is such a formula, could it be applied to solar systems in which there is more than one central star and/or more than one moon orbiting the planet?


texts: What lens should I use for my Raspberry Pi?

texts:
I am building myself a camera that attaches to the back of my Celestron NexStar 4 SE telescope and I am not sure what type of lens to choose to replace the stock lens on the Raspberry Pi camera. I bought this CS Mount and by mistake bought M12 lenses thinking it was a mount for M12 lenses but now I know CS mounts require bigger lenses than M12. So should I instead get a M12 mount and use M12 lenses or should I buy a CS lens and what kind if I am looking to do a high quality video/live stream?

Raspberry Pi Camera: https://www.adafruit.com/products/3099


texts: Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?

texts:
Is there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?

For example, could a planet with a 90° obliquity and large moon avoid such a situation?


texts: How can I clean my lenses without causing scratching or damages to the lens surface?

texts:
Sometimes you can be trying to observe very faint or very small objects in the sky and it wouldn't pay to have these obscured or marred by a scratch or dust on the lenses.

I keep to good practices and make sure to replace the cap on the lenses when finished in order to stop dust buildup but inevitably it will get a little dusty and dirty, taking this into consideration:

What steps do I need to take to ensure that my lenses are kept in top condition?

Can I simply use a damp cloth or sponge and dab the lenses or should I use a softer material, like someone with glasses might have a softer lens cleaner?

Do I require a special cleaning fluid or can a good quality clean be done without any additional cleaning agents?


texts: What is the nature of "rock vapor" in this description of the formation of the Moon?

texts:
The NPR News item MacArthur Fellow And Planetary Scientist Sarah Stewart Discusses How The Moon Was Formed and audio podcast begins:

Ari Shapiro, Host: Sarah Stewart likes to think about what happens when planets collide. She uses two actual cannons to simulate those massive impacts. Here's one firing in her lab at UC Davis.
Unidentified Person:  Firing in three, two, one.

Soundbite of Cannon FIring

Ari Shapiro, Host: Her work earned her a spot in this year's class of MacArthur Fellows. Many of us call it the genius grant. For years, experts have thought that Earth's moon formed after a large collision knocked off a bunch of rock. Stewart told me her research suggests a different story.
Planetary Scientist Sarah Stewart: During planet formation, when two bodies collide, there's so much energy released that most of these bodies are vaporized. That means that a rocky planet like Earth is mostly rock vapor.
Shapiro: What is rock vapor, and what does that have to do with our moon?
Stewart: Rock vapor is taking the rocks that we stand on and heating it up to the point where it becomes a gas. And when that occurs, the Earth becomes much larger because vapor is much less dense. And it extends out into this enormous object hundreds of times larger than the Earth today. And we proposed that our moon grows within the rock vapor of the Earth after a giant impact.
Shapiro: So the moon actually came from the Earth.
Stewart: The moon grows within the rock vapor of the Earth. And that gives the moon the same chemistry as the Earth.

We don't learn about "rock vapor" in Earth Science class, but I know it's got to be a lot hotter than the lava we see in the news. A significant fraction of Earth's crust is SiO₂ based and it's boiling point is roughly 3,000°C, and I have a hunch the temperatures involved here are much much higher than that. The kinetic energy associated with say a relative velocity of 40 km/s is roughly 8 eV per AMU, over 130 eV for every oxygen atom for example.
So does "rock vapor" start out as a highly ionized "rock plasma" with almost no covalent bonds remaining, or does most of the energy of the original impactor get transferred to a much greater mass of Earth?
Is there a good place to read about her and her students' MacArthur grant-getting research described in the podcast?


texts: Calculating the distance of objects using the Gaia DR1

texts:
The Gaia DR1 was released middle of September with ~1.1 billion objects. The schema contains right ascension, declination and parallax, which could be used to calculate Cartesian co-ordinates (xyz).

The overwhelming majority (>99.998%) of objects do not contain an entry for parallax. I suspect this needs to be computed using other columns (e.g. phot_g_mean_mag?).

How do you compute the parallax for an object when its not included?

The data model is documented here .


texts:
A while back NASA made a site called Pluto Time, where you can enter your address and find that "...moment near dawn and dusk each day, where the illumination on Earth matches that of high noon on Pluto."

Is there a generic formula where we can calculate this for any body in the solar system?

How about any body around any star?


texts: Are there any electrons inside the sun / a star?

texts:
Like the question says, are there electrons inside an active star, or has all the matter been so thoroughly ionized / plasmarized that the electrons are long gone? I ask because it would make sense when thinking about the magnetic field of a star; naked protons (neutrons are of no magnetic concern) would create a very one-way magnetic effect when circling inside the star, while protons + electrons would seem to counteract one another, magnetically.

Come to think of it, I guess the same question could be asked for the Earth's liquid core, considering its temperatures...?


texts:
Ok, so it's supposed that there is a black hole in the center of any galaxy, that makes my head explode because:

There is light in the center of the galaxy, but it is supposed that black holes, also attract light.
For a black hole to exist there should be a star explosion, so what size does the star needed to be to create such a galaxy.
Why does the black hole doesn't eat us, I mean what objects are pulling us away from the extreme gravity of the black hole.

I'm not god, I didn't study Astronomy, I'm just a kid fascinated by the Universe. (This question should be dumb for anyone who studied Astronomy)

But if you think my question is dumb, (which isn't) or if you have any recommendation for further asking, let me know!


texts: Why does a mirror bent 'like a potato chip' allow space telescopes to be smaller and have a wider field of view?

texts:
I was browsing NASA featured items and came across this - Out With the Old, In With the New: Telescope Mirrors Get New Shape

  Called freeform optics, this emerging mirror technology, brought about
  by advances in computer-controlled fabrication and testing, has
  triggered a sea change in optical engineering... the technology holds
  great promise for scientists who want to develop compact telescopes
  for CubeSat and other small satellites — an increasingly popular and
  cost-effective alternative to more traditional missions that are more
  expensive to build and launch.

Telescopes for cubesats?!

The article had this illustration, and I'm trying to figure out how that is converted into a clear image without distortions, and why they say it allows the telescope to be much more compact.

It was a short article that didn't even try to explain this, and when I went looking for other articles on the topic for non-experts I found zip. Perhaps this is very challenging to explain, but I thought I'd ask anyhow. I told an enthusiastic youth just a few weeks ago that it wasn't possible to launch a telescope capable of anything useful on a cubesat. Oops...


texts: Consider a semiregular variable with amplitude of 1.5 mag. Is it possible to explain brightness variations by purely dipole pulsations?


texts: How much competition there is for jobs in astronomy compared to other fields of science?

texts:
I will soon finish a master's degree in computer science. I have been interested in astronomy for some time, which has included playing around with a Newtonian reflector telescope and reading about CCD-cameras.

I checked some local universities, and was amazed that they have only 10 or so graduates each year (1-2 get a PhD and the rest a master's degree). How many jobs are there for these graduates? Compared to other fields, how tough is the competition in astronomy? Is it different for some relatively new areas, e.g. space neuroscience or astrobiology?

I am considering to apply for an astronomy PhD, so any input would be helpful.


texts: What does it mean for a planet to be just 300 kms across?

texts:
The recently discovered Planet Goblin is just 300 kms across. While I perfectly understand what it literally means, I'm having trouble wrapping this in my head. Does it mean I can imagine the planet as (approximately) a sphere for 300 kms diameter? That gives a radius of 150 kms, and thus a circumference of 942 kms.

A circumference of 942 kms means that the longest distance between any two points on the surface of the planet is just 471 kms -- That's just over 1.5 times the distance between London to Paris or 100 kms more than the distance between New York and Washington DC or about half the distance between St. Petersburg and Moscow.

Is the planet that small, really? Or am I missing something?


texts: Are there more stars than all the words ever spoken by humans?

texts:
A while ago I saw Neil deGrasse Tyson comparing the number of stars in the universe with the number of words spoken by all of humankind, ever since.

I realize both of these numbers are not strictly defined, but still, we can use our best observations together with our best guesses to find out which number is larger, and by how many magnitudes. It's a good example of making you realize the size of astronomical numbers in the true sense of the word.

What is your answer or guesstimate?


texts: Is there a formlua or equation to calculate a star's B-V index based on it's observed frequencies in the B and V spectrums ? I have unfortunately not been able to find anything...


texts:
I'm currently reading Planetary Geology, in which they state

When Ceres [...] was discovered in 1899, it was considered as the lost tenth planet.

Uranus and Neptune had been discovered, but Pluto wasn't know yet at the time. What were the nine planets back then? The bodies we now call planets + the Moon?


texts: Do some shooting stars NOT travel in a straight line?

texts: I saw what I assumed was a shooting star on December 21 (or 22) 2020 that moved in a straight line and then abruptly turned in an arc perpendicular to its original straight path. The brightness and duration was like any other shooting star that I’ve seen, but it’s path was not. Is this common?


texts: How galactic density falls using Oort constants

texts:
I am given the observations that Oort constants $A$ and $B$ are, respectively: $14.5 \text{km s}^{-1} \text{kpc}^{-1}$ and $-12 \text{km s}^{-1} \text{kpc}^{-1}$. From these, I am supposed to conclude that the galaxy density falls off as $\sim R^{-2}$. (Source of problem: Paper 2 Question 7 of 2016, Cambridge Astrophysics Tripos - see page 17.)
I don't see how I can pull this off, would appreciate any help.

In the earlier part of the question, I proved that at the solar location, it is true that
$$\frac{\partial^{2} \Phi}{\partial z^{2}}=4 \pi G \rho_{0}+2\left(A^{2}-B^{2}\right)$$
which might help somehow, but I don't see how.


texts: Smallest mass of star to be a black hole?

texts:
It seems to me that I forgot the smallest mass of a star and its angular momentum in order to form a black hole.

So I know that electron degeneracy pressure is overcome if the core is 1.4 solar masses, and neutron degeneracy pressure is overcome if the core is 3 solar masses, but if the neutron star is spinning fast enough, it can have a maximum mass of about 4 solar masses. But then, this is just the core of the star. How large does this star have to be in order to form a black hole, and how fast would its spin need to be in order to avoid forming a blitzar?

I've looked on google and bing but to no avail.

Help is appreciated!

Thank you!

Max0815

Please stop trying to make this a duplicate.

Why: How large does this star have to be in order to form a black hole, and how fast would its spin need to be in order to avoid forming a blitzar?


texts: Objection on artificial moon for lighting

texts:
Some days ago i read about China's artificial moon mission for lighting cities

In my junior classes i was taught the effect of Moon's gravity on tidal waves.
According to me this is a very dangerous mission this can cause floods due to additional gravitational force.
Am I wrong?Please explain.

  I had searched on Internet about this defect of China's artificial moon for lighting but i didn't found any result.Many astronomers are against this mission as this will disturb natural timing of flora and fauna.But no one has raised the point ,that it will disturb natural motion of tidal waves.


texts: A moon-sized object is running loose in the Solar System, perhaps after a planetary collision.  As it approaches a planet, it's presumably following an approximately hyperbolic path.  If it goes on past, it's still on the same hyperbola, on a curve mirroring its approach (presumably).  How can the planet ever capture it, whatever the body's velocity?  Why doesn't it either collide or go on past?


texts: This morning at 6AM I saw a line of lights coming out of Orion, moving across the North star then Big Dipper and disappearing into the early dawn.  I saw at least 30, no idea how many came before I noticed them.  They were not all evenly spaced, all moving at the same speed, very high, no sound. If these are Musk's satellites, why are they still sort of stacked, why are they moving in a NNE direction, and can I expect to see them again?


texts: Determine the moons of Jupiter through a telescope

texts:
I was doing my own "space exploration" last night with a telescope. Being a space noob I can't visually determine stars or planets (I know the moon, though), but I focused on one particularly bright one when I saw 4 smaller "stars" on each side. After a quick Google I learned I had discovered the moons of Jupiter!

I now know the moons I could see were Io, Europa, Ganymede, and Callisto. But which is which?

Is there an easy way to determine which Galilean moon is which?


texts: Air temperature range recommendation for observations in a summer night with an entry level telescope?

texts:
Recent nights where I try to make my first observations with the entry levell telescope Seben with 114 mm mirror it seems that for lenses less than 6 mm details go lost due to warm air refraction (as observed with the Moon contour).

Everywhere they say, it shouldn't be too warm: is it possible to recommend a rough temperature range where you could go for say 4 mm and still see details?

(Side note: the overall visibility index was about 77%).


texts: How are small objects automatically identified and their locations determined in digital images?

texts:
I have a large quantity of old digital images of low energy electron diffraction (LEED) patterns that I must process to identify and locate small, sometimes elongated gaussian-like blobs of a few pixels in width within a noisy and artifact-riddled background.
I'm currently reading up on Laplacian of Gaussian blob detection 1, 2, 3 and have started to implement the "roll-your-own" script in the first link; there are python packages like OpenCV and Scikit-image that have standard libraries for this as well and I believe they both have Laplacian of Gaussian blob detection, but I like to do it first myself to better understand what's going on.
Why are you asking this here in Astronomy SE?
Good question! Because this looks at least superficially a lot like what astronomers need to do when searching for objects in deep space imaging applications, and there may be some standard implementations in AstroPy or even lecture notes for Digital Imaging in Astronomy 101 courses.
In parallel with my brute force efforts, how might I compliment this work with existing astronomical imaging techniques to compare notes? It would be great if it turned out that some existing script or package searching for distant elliptical galaxies or weak gravitational lensing could be applied directly to these kinds of images!
Example image (most data has smaller pixels higher pixel density, but I need to process these low pixel count images as well):

The kinds of "spots" I'm looking for:

First try with Python implementation of Laplacian of Gaussian blob detection, haven't yet looked at generalizing to non-circular shapes, just ran the script in the link with a few small modifications.


texts: Traversing a proton within the Planck time

texts: If I could travel a super small distance (proton) in an even smaller time (Planck time), how long would it take me to cross the observable universe?


texts: Sunset on [Mountain] from [Viewing Point]

texts:
How do I get the days in this year when the sun will set exactly on top of Fuji as viewed from Enoshima.

I shamefully admit that I just want to take a nice picture of Fuji.


texts: Brightest star visible from Italy and Argentina

texts: A friend of mine tends to ask crazy question about everything. Today he ask me what is the brightest star that is visible on both the hemisphere and in particular from Italy and Argentina. I tried to ask wolframalpha but nothing came up. Thanks in advance.


texts: Difference in the baryon acoustic oscillation measurements

texts:
I understand from this Wikipedia page about baryon acoustic oscillations (BAOs). I can also see that BAO measurements were first detected using luminous red galaxy samples.

Now, many papers use galaxy clusters to measure the BAO signal. What is the advantage/difference between using galaxy samples and galaxy cluster samples to measure the BAO?

EDIT:

Here are some of the papers using galaxy clusters for BAO detection.

Estrada et al. 2008
Hong et al. 2012
Veropalumbo et al. 2014


texts: Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image?

texts:
@RobJeffries' answer to the question Does gravitational lensing provide time evolution information? points out that there can be a substantial different in arrival times of light from a given source seen in different images from a gravitational lens.

The linked paper there shows "$\Delta t$" values of the order of 30 days, but it is hard for me to understand what the actual observable is.

What I'm asking for here is (ideally) if there is a well defined event that a lay person could understand, something blinking or disappearing or brightening substantially that has already been seen in one image produced by a gravitational lens that has not yet been seen in one of the other images, and is expected to be seen in the (presumably near) future.

If something like this does not exist, a substitute could be a case where this has happened, and the second sighting of the same event was predicted, waited for, and observed on time.

I have no idea if this happens all the time, or has never happened yet.


texts: Calculating star radius from temperature and absolute magnitude - what am I missing?

texts:
In an attempt to visualise nearby stars, I've tried to get the star radius (measured in solar radii) using the equation provided on the following site:

http://cas.sdss.org/dr4/en/proj/advanced/hr/radius1.asp

Now though the equation seems to work fine for a star like Sirius, when I plug in the values for absolute magnitude and temperature for Barnard's star (according to wikipedia, 13.21 and 3134 K respectively) I get a radius of 0.0722. The radius provided by wikipedia is more than twice that value, at 0.196.

There are many potential culprits. Could it be floating point errors in the php code? The equation looks like this by the way:

$$\text{radius = pow(5800/3134, 2)} \times \text{pow(pow(2.512, (4.83 - 13.21)), 0.5})$$

Another possibility is that the equation is too simplistic, and there are other variables I need to take into account.

Any insights would be greatly appreciated!

Michael


texts: If universe is expanding why is the distance between planets not increasing?

texts: General relativity tells us space is expanding.Then why does the distance between planets and heavenly bodies increase?


texts: Gravitational red shift vs Doppler redshift: Is the universe really expanding?

texts:
Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted?

What I think I know thus far is this:

Redshift due to the Doppler effect of a moving object is happening due to universe expansion. Galaxies further away are speeding away from us faster than those close to us, hence having a stronger redshift effect.
Gravitational redshift is happening due to light "escaping" the gravitational pull of the source (star) and it has nothing to do with the movement of such source.


texts: Which will destroy the Earth first: the Sun or Jupiter?

texts:
The sun is expected to grow in brightness over time, slowly heating the Earth until the oceans evaporate, leaving the planet uninhabitable.
Jupiter is the source of the largest perturbations to Earth's orbit. In general, the 3 body problem (and higher) is not stable. So we can expect Jupiter to, eventually, perturb Earth's orbit until Earth falls into the sun or gets kicks completely out of the solar system.
So, which do we expect to kill the Earth first: solar baking or orbital chaos?


texts: Is there any possibility that a gas planet turns into a star

texts:
Since the sun is made of one of elements hydrogen
Why Saturn and jupiter doesnt turn into a star since they have a elements of hydrogen ?


texts: Are there any planned future observations of TRAPPIST-1 and its planets?

texts:
The recent discovery of new planets around the star TRAPPIST-1 happened by observations from 7 ground-based telescopes, as well as the Spitzer Space Telescope. The team of astronomers responsible has noted that there are many relevant parameters which still have large uncertainties, including orbital information and planetary mass. There's also some excitement about possible atmospheric composition.

Are there any definite planned future observations of the system? I assume that at some point it will be targeted by the James Webb Space Telescope, but that won't launch for another year and a half, and it has plenty of other targets.

I'm not looking for detailed information - I know that cannot be easily gathered - but if there are any general mentions, like this one about the Subaru Telescope and Planet Nine, that would be fantastic.


texts:
Why is the Hubble Telescope in space?

Do we get enhanced clarity and range by placing it in space?

What can it achieve from space that it could not achieve from Earth?


texts: Is intrastellar commonly used by astronomers to refer to objects within our solar system?

texts:
The CNET article Interstellar comet Borisov looks ordinary, making Oumuamua even weirder says:

  A paper published Monday in Nature Astronomy lays out the early data on Borisov, which is just the second-ever object seen visiting our solar system from beyond. While scientists will get a better look as the comet comes closer to Earth over the next several weeks, so far it looks to be the same color and size as most ordinary comets. Earlier research also revealed it's behaving in familiar ways with a tail containing some of the same toxic gases we expect from intrastellar comets.

(ArXiv)

Is the word intrastellar commonly used to refer to objects within our solar system by astronomers, or is it just the editors creative reversal of interstellar.

Along the same lines, would extrasolar be used by astronomers to refer to objects outside of our solar system?


texts: How to evaluate the fit of an isochrone to a stellar population?

texts:
Consider that I know the extinction, distance modulus, reddening, and metallicity for a particular star cluster.

I need to determine it's age from isochrone fitting.

After generating the required isochrones, what should be a parameter for the goodness of fit for the isochrone?

Is there something like a 'best fit line' that also exists for general curves?


texts: Computing the average hours of sunshine at given location&orientation

texts:
I made it my geeky aim to see which of two flats that we are considering moving into is sunnier. The first flat faces S and the second faces NNW; both are at the same height above ground and have similar terrain (buildings/trees) around.

Conventional wisdom would suggest the S-facing one is (much) sunnier, but I am not sure if this is really so, since I don't think it is the case that the Sun, when it's above the horizon, spends most of its time in the Southern-hemispace/hemifield.

Furthermore, I'd like to get a more quantitative estimate of how much direct sunlight each flat gets per day (averaged across seasons). How can I use tools available on the Internet (probably GoogleMaps-based) to find this out?

My only solution to date was to generate Sun trajectories (elliptics) for each flat, using the SunCalc.net website; these suggest the NNW-facing flat hardly ever sees the sun, except around the summer solstice. Is this a reliable estimate, or can anyone suggest another way to solve this riddle?


texts: How to caclulate the chinese Three Gorges Dam impact on Earth rotation?

texts:
According to this January 2005 NASA JPL News item NASA Details Earthquake Effects on the Earth, the Three Gorges Dam has slowed down Earth's rotation by 0.06 microseconds per day.

Having that weight of Earth is an estimate, and so is the volume / weight of water held by the dam and also that these two resulting figures are apart by several orders, how can the resulting deceleration be not only precise, but also calculated at all? The error margin must be much larger, then the result. Or not? How did NASA get the numbers so accurate?


texts: Missing Terms in Weinberg's treatment of perturbations on Newtonian Cosmology

texts:
I was reading Appendix F of Steven Weingberg's book "Cosmology". In this Appendix he works out the perturbations to a cosmological fluid described by non-relativistic hydrodynamics and Newtonian gravity.

It turns out that the first order perturbations satisfy,

$$
\frac{\partial \delta \rho }{\partial t } + 3 H \delta \rho + H \vec{X} \cdot \nabla \delta \rho + \bar{\rho} \nabla \cdot \vec{v} = 0, \qquad \tag{1}
$$

$$
\frac{\partial \delta \vec{v}}{\partial t } +  H \vec{X} \cdot \nabla \delta \vec{v} + H \delta \vec{v} = - \nabla \delta \phi, \qquad \tag{2}
$$

$$
\nabla^2 \delta \phi = 4\pi G \delta \rho. \qquad \tag{3}
$$

Weinberg applies the following Fourier transform to these equations,

$$ f(\vec{X},t)  = \int \exp \left(  \frac{i \vec{q} \cdot \vec{X}}{a} \right)  f_{\vec{q}}(t) \ \mathrm{d}^3\vec{q} $$,

where $f(\vec{X},t)$ is a place holder for $\delta \vec{v}, \delta \rho, $ and $\delta \phi$.

The resulting equations he gets are,

$$
\frac{\mathrm d \delta \rho_{\vec{q}}}{\mathrm d t } + 3 H \delta \rho_{\vec{q}} + \frac{i\bar{\rho}}{a}\ \vec{q} \cdot \delta \vec{v}_{\vec{q}} = 0 \qquad \tag{1'}$$

$$
\frac{\mathrm d \delta \vec{v}_{\vec{q}}}{\mathrm d t } +  H \delta \vec{v}_{\vec{q}} = -\frac{i}{a}\ \vec{q}  \delta \phi_{\vec{q}} \qquad \tag{2'}$$

$$
\vec{q}^2 \delta \phi_{\vec{q}} = -4\pi G a^2 \delta \rho_{\vec{q}} \qquad \tag{3'}$$.

For the most part these new equations can be obtained by making the substitution $\nabla \rightarrow i \vec{q}/a$.

My question : There doesn't seem to be any terms in the transformed equations which correspond to the terms $ H \vec{X} \cdot \nabla \delta \rho$ and $H \vec{X} \cdot \nabla \delta \vec{v}$. Weinberg makes no comment about their absence. Is anyone aware of a legitimate mathematical reason for these terms to disappear in the transformed equations?


texts: Why do we use filters in telescopes for astronomical imaging?

texts: I have read that if we image without a filter we get no information about the color or SED of objects.  Can anyone elaborate the reasons for using filters for imaging/photometry?  What happens if we image without a filter?


texts: Does precession affect this measurement?

texts:
I don't have the astronomy vocabulary to ask this question.   You can find a better picture at https://www.timeanddate.com/astronomy/axial-tilt-obliquity.html.
I want to know if the distance between points A & B on my graphic has a name, and if it would grow shorter or longer as the earth's rotation slows down.  Would this distance only reflect the 23° wobble in the rotation of earth or would it also reflect Precession of the Equinoxes.


texts: Spectral analysis of AGN (velocity dispersion of galaxy absorption, doppler shifts)

texts:
I was wondering what parameters I need to know/measure to calculate the velocity dispersion of a galaxy, specifically an AGN.

Also, I have spectra where there are blueshifted and redshifted components to certain emission lines in units of km/s.

For example, I have [O III] 5007Å but I have a blueshifted component centre at 5002Å and a redshifted component at 5011Å. I was wondering how I calculate the doppler shift again in units of km/s.

Many thanks.


texts: Why isn't interstellar medium pulled in towards nearest massive object?

texts: How does the ISM resist gravity? That's the only force acting on it, and all other particles seem to collect together to form stars. What makes the ISM so special among other particles?


texts: What is the difference between precession and axial tilt?

texts:
I'm a right that the difference is that precession indicates the direction of the inclination of the Earth'axis and the tilt is the quantity of this inclination? So that when there is no tilt there can't be any precession?

And are the inclination degrees of the precession and the tilt related or the same?

It seems that the precession causes different possible polarstar, but is the tilt also have effect on this?

Perhaps this above it not right, so what else is the difference? Is perhaps the precession just the changing of the tilt?


texts: Layman here with an affinity for astronomy, space and everything associated with it. I'm a big fan of the space oriented programs on the Discovery and Science channels and I was watching an episode recently that got me to thinking about the origins of Dark Matter (DM) and Dark Energy (DE). Do any of you know if any thought has been given to the creation of DM and DE as byproducts of space being created? As I understand it, as the universe expands it essentially creates space where nothing was before. To be honest, I know nothing about what that even means: creating space where nothing was before.


texts:
As it is obvious from the question title
is there any restriction or cases that we can see the binary stars as not in pairs

also is there any binary stars doesn't linked together by gravity ?

I know the definition of binary stars that it is  a pair of stars that revolve around their common center of mass but my question is about special cases if it is exist


texts: Why is there a zig-zag in elemental abundances?

texts:
In this answer to Is lithium considered a metal in astronomy? this image from Wikimedia of the abundances of elements in the universe was shared:

Credit: Wikimedia Commons user 28bytes, under C.C.-by-S.A.-3.0.
I thought it was fascinating that there is a near-constant zig-zag of abundancies.
Are these values accurate, and if so, what would cause this zig-zag?


texts: Gas giants put out a fair amount of heat from gravitational collapse, so there's bound to be quite a bit of upward moving winds.  If Carl Sagan's idea about aerial ecologies pans out, could larger organisms soar endlessly on thermal updrafts?  Are the updrafts outside storms thought to be strong, or like a mild breeze?  Got to wondering about this because the mostly H-He atmosphere would make buoyancy-only methods of staying airborne kind of tricky. Small stuff is easy to imagine, but larger stuff may need a boost.


texts:
This comment (below the question Is there any new water formed on, or brought to, Earth?) links to the 2002 Article in the New Scientist Was all the Earth’s water brought here by comets? which states:

Evidence that there is a constant rain of small comets, each a loose snowball held together by a carbon shell, first came in the 1980s from satellites that looked down on Earth and observed “atmospheric holes”- dark spots 50 to 100 kilometres across- that were appearing in the dayglow of the atmosphere. The dayglow is ultraviolet light emitted when sunlight interacts with the oxygen in the upper atmosphere. Water is the only common substance that could create such holes, and each could be made by a small comet containing between 20 and 40 tonnes of water that broke up into a cloud of vapour as it hit the atmosphere. The case for a cometary origin for the atmospheric holes grew in the 1990s when the trail of a cosmic snowball was picked up as it vaporised over the Atlantic by the visible imaging cameras on polar satellites.
From the number of atmospheric holes, it’s possible to calculate that the atmosphere is being hit by a 20 to 40-tonne snowball comet every 3 seconds. According to Frank, this is enough to add an inch of water to the Earth’s surface every 20,000 years. Over the 4.5-billion-year lifetime of the Earth they could have provided all the water in the oceans. (emphasis added)

The article also links to this University of Iowa page smallcomets.physics.uiowa.edu/.
Is this still believed to be happening? Have there been additional observations? Is the earth receiving water in the form of 20 to 40 ton comets ariving every three seconds?
Question: What ever happened to the "Small Comet Theory" of water influx on present-day Earth? Has it been discounted, modified, verified?


texts: Does Universal Time really track mean solar time?

texts:
At innumerable places on the net you can find the claim that leap seconds are inserted into UTC in order to make it track UT1 which again tracks mean solar time at the reference meridian.

However, when I tried to locate an actual definition of UT1, the closest I could find was IAU resolution B1.8 from 2000 which seems to define it implicitly from the following relationship with the Earth Rotation Angle:
$$ \theta = 2\pi\bigl(0.7790572732640+1.00273781191135448({\it JD}_{\rm UT1}-2451545.0)\bigr)$$

Here the magic constant 1.00273781191135448 appears to be derived from the ratio between the Earth's rotational period and the sidereal year -- but no provision for adjusting it for observed changes in that ratio seems to be made. (The least significant several digits of the constant must be wrong already).

As the Earth's rotation slows down, is UT1 therefore going to drift out of sync with mean solar time at the IERS reference meridian? Or am I missing something?


texts: Is there a name for this type of orbit of a natural satellite?

texts:
Is there a name for the orbit of a natural satellite of a planet who's period is the same as the rotational period of the planet, but the orbital motion has the opposite sense than the planet's rotation?

If there isn't an existing term or name, how would it at least be described, technically?

How much does the tidal effect affect satellites in a retrograde orbit?


texts: Why haven't more captured small moons been found?

texts:
Shouldn't captured moons have the same size distribution as asteroids? And asteroids are more common the smaller size they are. Moons are likely captured if they are in highly inclined orbits, and those moons should've originated as asteroids or Kuiper Belt objects. But there are only two moons, out of 194 known, smaller than 500 meters in radius. Aegaeon and S/2009 S1 both of Saturn. Although it is expected to exist over a million asteroids smaller than that. And all of Pluto's moons were large enough to be found before New Horizons arrived (sorry Alan Stern, no moon for you!)

Is this purely an observational bias?
Is it expected that the planets are surrounded by a myriad of moons too small to have been detected yet, from hundreds of meters down to dust grains?
Do they all somehow gather into planar rings below a certain size? (I think the main line is that a ring system forms as a result of a single collision or tidal crunching event).
Or what mechanism makes them lack small to tiny moons and dust?

How would this asteroid size frequency plot compare to a moon size frequency plot?


texts: What is the underwater temperature of Europa?

texts:
If Europa has an oxygen atmosphere with a water mantle, is it possible that there could be life under the crust of Europa ice on the ocean where it is warmer? What could be the temperature under the ice?

Image of all the water of Earth beside it in a sphere.


texts: Modifying Heisenberg's unified field theory with gravity

texts:
How would Hisenberg's unified field equations be represented if gravity is incorporated. Would it result in a case similar to the Heisenberg-Ivanenkov equation, or am I just confused here?

I would really appreciate if the Heisenberg-Ivanenkov equation's essence is explained as there is no firm online source to provide more information.


texts: How are the masses of celestial bodies determined?

texts: I was scrolling through the list of moons of Jupiter and I wondered how astronomers where able to determine the masses of those objects. When I tried to google it I meanly found results of people deriving the mass of Jupiter from the masses of its moons using Kepler's laws. So the mass of celestial bodies with satellite(s) can be estimated this way. But what about the rest? Or are they all derived from the trajectories of man-made satellites passing near them?


texts: How to compute Ascension / Descension cycle of the Moon

texts:
I am struggling to find out an information about how to determine ascending/descending cycle of the Moon.

I can find from this source and a bunch of others, that Moon begins to descend when reaches Gemini and minimum when reaches Sagittarius.

I tried to do a simple comparison using flatlib library:

from flatlib import const
from flatlib.datetime import Datetime
from flatlib.geopos import GeoPos
from flatlib.chart import Chart

d1 = Datetime("2020/1/21")
d2 = Datetime("2020/1/22")
d3 = Datetime("2020/1/23")
pos = GeoPos('50n06', '14e24') #I concentrate to a specific place on northern hemisphere
c1 = Chart(d1, pos)
c2 = Chart(d2, pos)
c3 = Chart(d3, pos)

m1 = c1.get(const.MOON)
m2 = c2.get(const.MOON)
m3 = c3.get(const.MOON)
print(m1)
print(m2)
print(m3)

Which prints:

Moon Sagittarius +14:07:19 +13:16:13
Moon Sagittarius +27:17:06 +13:03:28
Moon Capricorn +10:14:25 +12:51:13

Am I right that moon is ascending during these days (21-23rd Jan 2020) as it moves from Sagittarius to Capricorn and further to Gemini?

I am aware of this answer, but I am not exactly sure if it deals with same problematics.


texts: In space, can you tell that you're flying sideways?

texts:
Imagine a vehicle like the dragon capsule, but the chair is on the bottom and facing forward, and the thrusters are directly behind it as illustrated above. When flying in space towards some planet, can the astronauts tell they're facing down and flying not forward relative to the direction they're facing?
Edit
To add clarity, my question is not about the logistics of space travel, but the physics of the drawing. Assuming a craft like the one above, with thrusters on or off, the craft flying in the direction of the arrow, and the astronaut sitting as depicted... Would he/she be able to tell that they're flying "headfirst" as opposed to the traditional concept of "forward" like you would when flying an airplane?


texts: Galactic mass estimation from apparent magnitude and distance

texts:
Can we estimate the order of the total mass of any galaxy from the apparent magnitude and its distance to us? Just like
\begin{equation}
M_{galaxy}=c\times 10^{8}M_{\odot },
\end{equation}
where $c$ is a constant (can be arbitrary or ignored, the order is important).
For example mass of the Tucana Dwarf of the Local group isn't known. But its apparent magnitude is 15.7 and average distance is $8.8\times10^{5}pc$. How can I estimate its approximate total mass?


texts: What are the aberrations of an SCT? And how can they be eliminated?

texts: The Schmidt-Cassegrain telescope is amazing! It is compact, suitable for astrophotography ,and it requires little to no collimation. However, the SCT has some inherent optical issues. What are they? What are their causes? and how can they be eliminated?


texts:
I came across a website saying that classical T Tauris have an "EW(Hα) > 5 angstroms".

Does anybody know what "EW" means?

Thanks.


texts: Would the dynamic pressure of the Sun’s solar wind be strong enough to trap plasma ions within an open container?

texts: If you were to place a long cylinder, open at one end and closed at the other end, and position this cylinder so that the open end is facing the Sun, and then you were to inject plasma ions, such as oxygen ions, into the cylinder near the closed end, would the solar wind entering the open end of the cylinder be strong enough to keep the oxygen ions pinned against the closed end of the cylinder, effectively trapping them there? How close to the Sun would this cylinder need to be for the solar wind to be strong enough to 'entrap' these oxygen ions?


texts:
The BBC News article UK will lead European exoplanet mission says:

Steady platform
And one aspect that would work in Ariel's favour is the absence of any moving parts in its build, commented Plato team-member Dr Don Pollaco from Warwick University, UK.
"The issue with all of these planet experiments is that the signals you are looking for are so incredibly small that any systematics in the instrument itself will dominate the signal," he explained.
"And the systematics are often associated with bits that move. So the great thing about Ariel is that it is fixed-format - nothing changes," he told BBC News.

Question: What's fixed in Ariel that is moving in other planet-hunting space telescopes? Is it only aspects of the satellite's telescope and payload module, or does this difference include aspects of the satellite's attitude control system and other things in the service module as well? See ESA's Ariel.


texts: If the Higgs field only formed after the Big Bang, how was hydrogen formed?

texts:
These two statements seem to conflict, but since we're here they can't:

Electrically charged particles cannot be massless.
Hydrogen was created at the moment of the Big Bang.

However, the Higgs field theory states that the field was only created AFTER the Big Bang. This implies that all particles from which hydrogen could be formed were massless. Hydrogen consists of 2 charged particles.

If you could provide an answer without complex math I would really appreciate it.


texts: Is there a relation between mass, radius, and luminosity in deuterium-burning brown dwarfs?

texts:
I'm a worldbuilder and my setting has a lot of brown dwarfs.

While I'm trying to keep my setting as science-compliant as possible, I can't seem to find any resources for brown dwarfs like there are for main sequence stars, just basic encyclopedia pages describing what brown dwarfs are.

I do know that brown dwarfs undergo deuterium fusion for a short period of time after they form, cf. Wikipedia's Brown dwarf; deuterium fusion.

Does that process lead to a mass-radius-luminosity relation like hydrogen fusion does in main sequence stars?


texts:
I just stumbled across the following answer "update" from 2013:

This just in, recent observations have ruled out the possibility that SMBHs gain mass only through merging with other black holes. For more, see this Astronomy.com article.

Question: How do we know that supermassive black holes can gain mass by means other than merging with other supermassive black holes? I can't figure it out from the linked Astronomy.com article. In fact I can barely read it behind all the blinking advertisements that it now displays (and probably didn't back in 2013)

Potentially related:

Why can't supermassive black holes merge? (or can they?)
How do two supermassive black holes reach "the last parsec" in merging galaxies?
Why do we believe that the super massive black holes at the centers of two merging galaxies would themselves merge?
What enhances the capture and merge rates of pairs of small black holes orbiting around supermassive black holes?
Why would the merger of spinning black holes within the accretion disk of a supermassive black hole cause them to "shoot straight up" out of the disk?


texts: Why isn't the moon dark in a solar eclipse?

texts:
In the following partial solar eclipse, the moon is "invisible" rather than being dark.  By contrast, if someone stands between my view and the sun, they will appear as a dark figure instead of invisible.

Why doesn't the moon appear as a dark circle instead of being invisible?


texts: Predicting accurate time of local sunrise in mountainous area?

texts:
Is there any software which will tell me accurately at what moment any part of the solar disk will become from a specific point on the ground taking account of terrain. I feel like Google maps should have the terrain data I need, and the rest is geometry, but it looks like quite a bit of work, so I wondered if it already existed.

Specifically, I am interested in when a viewer 1.5m above local ground level at latitude 46.497300, longitude 7.714651 will first see direct sunlight on the morning of 1 August 2023, taking account of the surrounding mountains. Ideally I'd like to know how that varies with height above the ground (1-2m) and for locations within 10-20m around that location (in other words, how and when the shadow of the mountains moves off that area).


texts: Black dot visible when looking into the telescope

texts:
A few weeks a go I bought a telescope.
The problem is I am a total beginner. I was able to setup the telescope correctly and I already saw the moon very clearly. Then I moved on to jupiter. When I looked through the telescope a black dot was visible in the middle of Jupiter. I have already turned the focusing wheel but then Jupiter became smaller and smaller and the point became smaller. But even when I turned the eyepiece all the way out the dot was still visible and jupiter was hardly visible.


texts:
I have a question concerning how Hawking radiation works.

As I understand, a pair of particle-antiparticle may pop to existence near the event horizon (from a virtual particle).

Then it might happen that the negative particle (antimatter) gets captured by the black hole whereas the positive particle (matter) escapes.

This results in a net loss of the black hole mass. If you repeat this process an astonishing number of times the Black Hole might end up completely evaporating.

Am I right so far? (Even if the explanation is not very mathematical)

My question then is:

This assumes that when a pair particle-antiparticle is created, a bias towards antiparticles being captured and particles escaping must exist.

Otherwise, the mass of the black hole might fluctuate, but in average for big numbers of pairs, equal percentage of particles and antiparticles would be captured/escape.

So, is there really a bias needed for the black hole to loose mass, or is it something wrong about my understanding of Hawking radiation?

Thanks


texts: What simple mathematical function would reasonably well simulate sunlight intensity (disregarding weather) from dawn till dusk in relative numbers, 0-100 %. Are there significant differences (apart from maximum power and daylight duration) between temperate winter, summer or tropical days? The goal is more natural LED lighting for captive wild animals.


texts: Calculating orbits using observational data

texts:
How did astronomers in the 18th and 19th centuries used to calculate a comet's or planet's orbit using observational data, given that this data is relative to a non static reference point (i.e. the Earth)?

For instance, here one can find the measurements of Mars' declination by Tycho Brahe throughout two decades. Not only it seems very difficult to me to deduce the right curve from the original observations points, but also the peaks of the curve (which resembles a sinusoid) do not seem perfectly equally distant from each other.


texts: I'm obviously a novice. I see a star in the eastern sky every night. It is quite large and impressive. How can I identify it. Thank you.


texts: If Jupiter would stop rotating, would its atmosphere become homogeneous and single coloured?

texts:
Looking at pictures of Jupiter, there are many different colours and patterns. I imagine that the rotation has much to do with this, since there are horizontal "bands" across the planet along the direction of rotation.

If the rotation would slow down and eventually stop, would the atmosphere get mixed and even out over time until we could only see a fuzzy brown (?) color but no color shifts or other patterns on the surface?


texts: How can I create tracks of the planet's orbits on my computer?

texts:
I'm wondering if there's any good computer software for tracking the orbits of planets over time. I like to see the orbit's trails against the sky background.

I'd prefer something that's free and of a good quality.

I've already tried Google Earth, but it doesn't seem to be able to do this.


texts: How many parent stars contributed to our solar system?

texts:
All of the stuff that isn't hydrogen and helium (which came from the Big Bang), that coalesced to form our solar system (the iron, the sulfur, the water, and so forth) all came from previous generations of stars that went supernova, merging neutron stars, etc. All that material collected together and formed our solar system...

From roughly how many stars did that material come from? Is there any way to know?


texts:
Would a lunar eclipse seen from low (or even high) Earth orbit look different to the naked eye than it does from the surface of the Earth?

The only image I could find taken from orbit was the photo by Alexander Gerst from the ISS.  "The slight hue of blue is actually the Earth's atmosphere, just before the Moon is diving into it."


texts: When will Sirius be closest to the solar system?

texts: Sirius is currently approaching the solar system, at a rate of 5.5 km/s, consequently in the future it will be closer and therefore brighter. When will Sirius pass closest to the solar system? How far will it then be from the sun, and what magnitude will it reach?


texts: When the moon eclipses the sun what direction is darkened first: left or right?

texts:
I saw the question and answer for the explanation of the direction of the moon's eclipse from left to right, but what about the direction of the moon as it passes over or between Earth and the sun?

Does the moon always pass from the right to the left or from the left to the right as it covers the sun; if you live above the equator?

Or does this change? Can it change? August 2017 the USA will have a total eclipse of the sun for the first time in decades.


texts: How to determine the age of an old galaxy?

texts: Recently a galaxy A1689B11 was discovered, having an age of 11 billion years. How that age was determined? News sources reported that some cutting edge technology with gravitational lensing was used. Can anyone explain the exact procedure?


texts: At Mars' equator how long does twilight last?

texts: With Mars' thinner atmosphere I'm assuming twilight would not last as long compared to the duration on Earth.  Has there been any determination of the length of twilight on Mars at the equator or any other latitude?


texts: Is it possible for a star to return in the main sequence?

texts: Is it possible for a star to return to the main sequence after entered in the post-main sequence phase? I have no clue if there's a mechanism such as acquiring hydrogen from from the environment or from a substellar body might bring again the star into the main sequence. Was it ever explored as a possibility?


texts: What is the current accepted theory as to why Venus has a slow retrograde rotation?

texts:
According to this NASA overview, the planet Venus is unique (amongst the major planets), Venus has a slow retrograde axial rotation, taking 243 Earth days to make one rotation (which is longer than its orbital revolution).

What is the current accepted theory as to why (and how) Venus developed this anomalous slow retrograde axial rotation?


texts: In sky surveys, what does inverse variation really mean? How do we use inverse variation to remove noise?

texts: I am trying to work on data from a .fits file and it has an IVAR header. How can I use inverse variation information along with the actual signal data to get better results or reduce noise?


texts: Does the sun have a feature like the red spot on Jupiter?

texts: Does the sun have a feature or prominence like the red spot on Jupiter? Is there a feature that will remain as long as the red spot?  Maybe beneath the surface?


texts: Does the holographic principle contradict eternal inflation?

texts:
As it is for example explained here, Andrei Linde's chaotic inflation is among the potential winners or survivors of the spring cleaning induced by the potential detection of primoridal gravitational waves. As this type of inflation is eternal, the new data might also lend some updraft to the multiverse business etc ...

But I always thought that because of the holographic principle, which means when applied to the exponentially expanding universe that stuff moving away can be thought of as being attracted to the cosmic horizon which takes to role of a black hole horizon, it does not make sense to talk about regions or any other universes beyond the cosmic horizon anyway.

So, does the holographic principle contradict eternal inflation as it arises for example from Linde's chaotic inflation? What does the detaction of primordial gravitational waves then mean when taking the holographic principle into account?


texts:
Could the expansion of universe be a side effect of gravity? I mean maybe gravity "attracts things" at a "small" distances and repells them at "larger" distances?

Do we have any theory/hypothesis/paper on this topic? Is it possible to prove or disprove?

UPD.

There is another, more clear way to ask the same question:

  Could gravity have a repulsive term that dominates at cosmological
  distances and could it be such a term that causes (accelerated)
  expansion?

Thanks to @uhoh and @Richard, for helping to clarify question a bit.


texts: Star Map Vs Star Catalogue vs Planetarium Software

texts:
What is the difference between a star map, star catalogue and the sky provided by planetarium software? I have read the wiki but was having a hard time understanding how the data, accuracy and detail for the star sky created out of each of these sources vary.
For example catalogues have properly studied specific stars, I assume, this means they will have the highest accuracy. But they are having only a small number of stars compared to a software like Stellarium. But I couldn't understand about the data accuracy or precision details of such software. Looking to understand more on the data accuracy and precision of skies. Thanks in advance.


texts: Thought experiment about the outskirts of the universe

texts:
Suppose I aim at some object that is 13 billion light years away from Earth. Let's assume I have a twin that pilots a ship that travels in infinite speed, meaning that he can reach that object  and get back here in a split second. On the other hand I'm the poor brother, and I own a ship with top speed of only at 99.9% of c.

We leave earth at the same time, with the same destination. My ship accelerates at constant rate for a full day until we reach max speed, then we enjoy the travel without accelerating for a second time.

1) how long will it take me to meet my brother, and how older will he be?
2) what will be the age of the universe, according to me?
3) what will be my current speed relative to surrounding objects before decelerating? Would I be able to accelerate and reach max speed again? If yes, what's the point of accelerating later rather than sooner, and having a top speed after all?

4) And a plot twist: suppose that while in travel I build a second ship exactly the same as mine. When we're about to arrive we choose a distant point 13 billion light years away in the same direction, and I send a friend on it, who accelerates until he reaches 99.9% of c relative to me. If we repeat that for N times, will we ever reach "free space" where matter didn't reach yet, or some other cosmologically interesting place? How does it look like there? If not, a) can we tinker with any parameters in order to do it "right"? b) any other plans on getting there?

I understand relativity from what I learned in college (long time ago), is there any other theory needed to understand such traveling questions?


texts: Could non-supernova carbon, oxygen, or silicon flashes be observed?

texts:
I was reading about the helium flash, the short but sudden onset of helium fusion in certain red giant stars. As I understand, the upper (nondegenerate) layers of the star absorb the energy as they quickly expand, which leads to the stabilization of the core as thermal pressure takes over, leading to the period of helium burning.

I was curious as to whether this could be generalized to the onset of fusion of heavier elements later in a more massive star's life, and I came across a reference to a hypothetical silicon flash in Woosley & Heger (2015). More digging led me to a passage in Fundamental Astronomy (page 250), which states

  In stars with masses around 10 $M_\odot$ either carbon or oxygen may be ignited explosively just like helium in relatively low-mass stars; there is a carbon or oxygen flash. This is much more powerful than the helium flash, and may make the star explode as a supernova.

Let's say that a star undergoes a relatively low-power carbon, oxygen, or silicon flash, and enough energy is absorbed by the outer layers such that the star does not undergo a supernova. Would enough energy escape the outer layers of the star so that we be able to detect the flash using optical or neutrino telescopes? Obviously, this is distance-dependent, so I'll say that the hypothetical star is within five parsecs of Earth.

As another way to put the question, how luminous would the flash be?


texts: Just after the Big Bang, was the space, in its entirety, filled with Hot gas?

texts:
After the Big bang occurred, was the space filled with hot gas totally?

If there's any problem in my question please inform me. Thanks!


texts: To anyone's knowledge, has there ever been an object that approached the earth and was captured into an orbit? Is it thought that there might be such objects simply too small to spot or just not discovered yet?


texts: What could be past the particle horizon?

texts:
Forgive any kind of "dumb" question I may ask as this is a new interest of mine and I know it's purely hypothetical.

If one were able to surpass light speed and the expansion of space to go beyond the particle horizon, what could be out there? Could it just be an empty void? Could it loop around to the other side of the particle horizon? I'd love to read about any kind of theories or research done on this subject.


texts: What more could be learned from a rare astronomical event if we knew precisely when it would occur?

texts:
This is actually related to a question I recently asked on Worldbuilding, but seemed more appropriately asked here.

To keep this from being too broad in scope, let's assume that someone figured out the exact moment that Eta Carinae will go supernova (I wouldn't hold it against anyone if they suggested a more scientifically interesting event).

Due to this foreknowledge, we could point every telescope we have in its direction for the main event.  Is there any science we know we could do/learn from this event that we wouldn't get by reacting to it after the fact?  I know such an event would generate data for a century or more to come, but I'm interest in the moment of the explosion.

Somewhat related, is there anything we would/could do now to prepare for it if this event were going to happen today?